1. Field of the Invention
The present invention relates to a focal length transitional method, an auxiliary lens for transiting focal lengths, and a lens system and a finder having a focal length transitional function.
2. Description of the Related Art
A varifocal lens system has a function for changing focal lengths by changing distances between lens groups while the position of an image surface is constantly held. In this varifocal lens system, an auxiliary lens is additionally used to provide a focal length shorter than a shortest focal length and provide a focal length longer than a longest focal length. Such a technique for changing or transiting the focal lengths is shown in Japanese Patent Application Laying Open (KOKAI) No. 60-168114, Japanese Patent Publication (KOKOKU) No. 61-40965, etc.
When the focal lengths of the lens system are transited by inserting and arranging the auxiliary lens between constructional lens groups, a space for inserting the auxiliary lens is generally disposed in advance within the varifocal lens system when the structure of lenses is designed. Therefore, there is a problem that an entire length of the varifocal lens system is increased.